Isolation and characterization of T cell receptors for antigens is of great importance because little is known about the molecular underpinnings of the recognition systems on the cell surface of thymus derived lymphocytes. We have chosen to study the receptors for human histocompatibility antigens (HLA-A and B) on cytotoxic T lymphocytes, because of 1) the paramount importance of the products of the major histocompatibility complex in cellular immunology, 2) accessibility to biochemical studies of the process of T cell killing, 3) the availability of large quantities of well characterized human histocompatibility antigens. The intention of the proposed studies is to apply techniques developed in cell surface receptor research such as radioreceptor assay, photo-affinity labelling and affinitychromatography to describe properties of the T cell receptor for HLA antigens. It is expected that these studies will not only be of theoretical but also of clinical importance in transplantation and autoimmune diseases.